Official document is somewhat persuasive, on reflection (4)
I believe the answer is:
visa
'official document' is the definition.
(travel document)
'somewhat persuasive on reflection' is the wordplay.
'somewhat' indicates a hidden word.
'on reflection' says the letters should be written backwards.
'asiv' can be found hidden inside 'persuasive'.
'asiv' written backwards gives 'VISA'.
'is' acts as a link.
(Other definitions for visa that I've seen before include "Travel document is required to enter Virginia" , "giving you access to capital?" , "Travel stamp in passport" , "ID" , "travel authority" .)